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Coffee consumption and CYP1A2 genotype in relation to bone mineral density of the proximal femur in elderly men and women: a cohort study

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Drinking coffee has been linked to reduced calcium conservation, but it is less clear whether it leads to sustained bone mineral loss and if individual predisposition for caffeine metabolism might be important in this context. Therefore, the relation between consumption of coffee and bone mineral density (BMD) at the proximal femur in men and women was studied, taking into account, for the first time, genotypes for cytochrome P450 1A2 (CYP1A2) associated with metabolism of caffeine. Methods Dietary intakes of 359 men and 358 women (aged 72 years), participants of the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS), were assessed by a 7-day food diary. Two years later, BMD for total proximal femur, femoral neck and trochanteric regions of the proximal femur were measured by Dual-energy X-ray absorptiometry (DXA). Genotypes of CYP1A2 were determined. Adjusted means of BMD for each category of coffee consumption were calculated. Results Men consuming 4 cups of coffee or more per day had 4% lower BMD at the proximal femur (p = 0.04) compared with low or non-consumers of coffee. This difference was not observed in women. In high consumers of coffee, those with rapid metabolism of caffeine (C/C genotype) had lower BMD at the femoral neck (p = 0.01) and at the trochanter (p = 0.03) than slow metabolizers (T/T and C/T genotypes). Calcium intake did not modify the relation between coffee and BMD. Conclusion High consumption of coffee seems to contribute to a reduction in BMD of the proximal femur in elderly men, but not in women. BMD was lower in high consumers of coffee with rapid metabolism of caffeine, suggesting that rapid metabolizers of caffeine may constitute a risk group for bone loss induced by coffee.
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Hallström et al. Nutrition & Metabolism 2010, 7:12
RESEARCH Open Access
Coffee consumption and CYP1A2 genotype in
relation to bone mineral density of the proximal
femur in elderly men and women: a cohort study
1,6* 2,3 1 4 5 2,6Helena Hallström , Håkan Melhus , Anders Glynn , Lars Lind , Ann-Christine Syvänen , Karl Michaëlsson
Background: Drinking coffee has been linked to reduced calcium conservation, but it is less clear whether it leads
to sustained bone mineral loss and if individual predisposition for caffeine metabolism might be important in this
context. Therefore, the relation between consumption of coffee and bone mineral density (BMD) at the proximal
femur in men and women was studied, taking into account, for the first time, genotypes for cytochrome P450 1A2
(CYP1A2) associated with metabolism of caffeine.
Methods: Dietary intakes of 359 men and 358 women (aged 72 years), participants of the Prospective Investigation
of the Vasculature in Uppsala Seniors (PIVUS), were assessed by a 7-day food diary. Two years later, BMD for total
proximal femur, femoral neck and trochanteric regions of the proximal femur were measured by Dual-energy X-ray
absorptiometry (DXA). Genotypes of CYP1A2 were determined. Adjusted means of BMD for each category of coffee
consumption were calculated.
Results: Men consuming 4 cups of coffee or more per day had 4% lower BMD at the proximal femur (p = 0.04)
compared with low or non-consumers of coffee. This difference was not observed in women. In high consumers
of coffee, those with rapid metabolism of caffeine (C/C genotype) had lower BMD at the femoral neck (p = 0.01)
and at the trochanter (p = 0.03) than slow metabolizers (T/T and C/T genotypes). Calcium intake did not modify
the relation between coffee and BMD.
Conclusion: High consumption of coffee seems to contribute to a reduction in BMD of the proximal femur in
elderly men, but not in women. BMD was lower in high consumers of coffee with rapid metabolism of caffeine,
suggesting that rapid metabolizers of caffeine may constitute a risk group for bone loss induced by coffee.
Introduction density (BMD) in both women [6-14] and men
Caffeine is the most widely used central nervous system [12,15-21] have been conflicting, which might be
stimulant in the world. There are several conceivable explained by differences in sample size, method of data
health benefits with the intake of caffeine-containing collection and amount of coffee consumed. In addition,
beverages but they can also produce unwanted health it has been suggested that a high caffeine intake is only
consequences. Caffeine increases calcium excretion [1-4] deleterious for bone health when calcium intake is low
and decreases intestinal calcium absorption [5], with 5 [22]. In Sweden, consumption of coffee and thus caf-
mg net loss of calcium per cup of coffee [1]. A high feine intake is high in a substantial proportion of the
intake of coffee could therefore also induce loss of bone population, making this setting suitable to study the
mineral. relation between coffee and BMD and subsequently the
Results from epidemiological studies investigating the risk of osteoporosis.
relation between coffee consumption and bone mineral Several enzymes are involved in the metabolism of
caffeine, but the most important is cytochrome P450
* Correspondence: heha@slv.se 3pathway is a N -demethylation, which results in the for-1Research and Development Department, Toxicology Division, National Food
mation of 1,7-dimethylxanthine, i.e., paraxanthine [23].Administration, Box 622, SE-751 26 Uppsala, Sweden
© 2010 Hallström et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.Hallström et al. Nutrition & Metabolism 2010, 7:12 Page 2 of 9
A wide variability in CYP1A2 activity between indivi- food diary after instructions from a dietician. The pre-
duals has been observed [24]. Depending on genotype, coded food diary had been prepared and previously used
some individuals are regarded as slow metabolizers of by the Swedish National Food Administration (NFA)
caffeine, while some are regarded as rapid metabolizers and Statistics Sweden in a food survey of 3,000 house-
[25,26]. There is also a gender difference with men, on holds in 1989 [30]. The questionnaire has been validated
average, having higher CYP1A2 activity [27]. To our [30,31]. The menu book included written instructions
knowledge, no study has yet investigated how coffee with an example on how to complete the book. The
consumption could affect BMD in relation to the rate of record sheets started with “day 1” followed by six addi-
caffeine metabolism determined by the genetic constitu- tional days. For each meal (breakfast, lunch, dinner and
tion of the individuals consuming coffee. However, in a snacks), the respondent was asked to specify where and
study of coffee intake, CYP1A2 genotype and risk of at what time the meal was eaten. The amounts con-
myocardial infarction coffee was associated with an sumed were reported in household measurements or
increased risk of nonfatal myocardial infarction only in specified as portion sizes according to a photograph
participants regarded as slow metabolizers of caffeine showing four portion sizes. Coffee and tea consumption
[26]. Accordingly, in the present study we hypothesize was registered six times daily (breakfast, lunch, supper,
that the participants’ genotype for cytochrome CYP1A2 between meals and in the evening).
could modify the relation between coffee consumption The daily intake of energy, caffeine, alcohol and
and BMD. This is because caffeine exposure of the body selected nutrients including calcium, vitamin D and A,
will last for longer periods in the “slow” caffeine meta- was calculated using a computerized program and infor-
bolizers than in the “rapid” caffeine metabolizers. Until mation about energy and nutrient contents of foods
now, however, the possibility of modulation by genotype from a database from the National Food Administration
for CYP1A2 has not been considered in studies of coffee that included 1,500 food items, drinks and recipes. Fil-
consumption and BMD. tered or brewed coffee is the most popular type of cof-
The principal aim of this study was to investigate the fee in the Nordic countries, while it should be noted
relation between consumption of coffee and BMD of the that decaffeinated coffee and tea are not typically con-
proximal femur in a population-based cohort of 70- sumed in the Swedish diet [23]. One cup of filtered cof-
year-old Swedish men and women. A secondary aim fee (150 mL) was estimated to contain approximately
was to study whether the relation between consumption 100 mg caffeine [23]. One cup of tea (200 mL) was esti-
of coffee and BMD in the cohort was modified by the mated to contain about 50 mg of caffeine [23]. No ana-
participants’ genotype for cytochrome P450 1A2 lyses of caffeine content of the consumed coffee and tea
(CYP1A2). were performed.
Materials and methods Measurement of bone mineral density at the proximal
Subjects femur
The Prospective Investigation of the Vasculature in On average, 2 years after the baseline investigation, 898
Uppsala Seniors (PIVUS) [28] has been described pre- of 1,016 cohort members agreed to undergo measure-
2viously [29]. In brief, all 70-year-old individuals residing ments of BMD (g/cm ) for total proximal femur,
in Uppsala, Sweden, in 2001-2004 were eligible. Of femoral neck and trochanteric regions of the proximal
these individuals, 2,025 were randomly selected and femur by DXA (DPX Prodigy, Lunar corp., Madison,
invited to participate within 2 months of their 70th WI, USA). This is the site of the most serious conse-
birthday from April 2001 to June 2004. Of those invited, quences of osteoporosis - the hip fracture [32], which
1,016 (50%) eventually participated in the study. The constitutes two main fracture categories: the femoral
participants were examined by measurements of blood neck and the trochanteric femoral fracture. When
pressure and anthropometry, blood sampling after an applicable, both extremities were used in the calculation.
overnight fast, routine medical history and assessment By triple measurements in 15 participants, the precision
of BMD using Dual-energy X-ray absorptiometry (DXA) error of the DXA measurements of total proximal femur
as described below. The study was approved by the in our laboratory has been calculated to be about 0.7%.
Ethics Committee of Uppsala University and all partici-
pants gave their written informed consent. Genotyping of CYP1A2
A common polymorphism in both Caucasians and
Dietary assessments Asians is the variation of the nucleotide at position -163
Dietary habits were registered in 850 (84%) of the parti- in intron 1 of the CYP1A2 gene. The C allele at position
cipants. Each participant recorded his or her food con- -163 in the CYP1A2 gene is considered to confer
sumption during 7 consecutive days using a pre-coded decreased inducibility to the enzyme [24,33,34].Hallström et al. Nutrition & Metabolism 2010, 7:12 Page 3 of 9
Consequently, carriers of a C allele at this position are Our hypothesis that the participants’ CYP1A2 genotype
regarded as “slow” metabolizers of caffeine [24,33,34]. could potentially modify the relation between coffee
Enzyme inducibility is increased by a substitution of C intake and BMD was tested in high consumers (both
with A at position -163 in the CYP1A2 gene and homo- sexes) of coffee (4 cups or more per day). “Slow” metabo-
zygote carriers of the mutated allele are considered lizers were defined as participants with genotypes C/T
“rapid” caffeine metabolizers of caffeine. In a previous (40.6%) or T/T (10.7%) while “rapid” metabolizers were
study, polymorphisms of rs762551 in the CYP1A2 gene those with genotype C/C (48.7%). Average multivariable-
have been shown to influence the association between adjusted BMD values of “slow” and “rapid” metabolizers
coffee intake and myocardial infarction [26]. However, were compared. To eliminate potential inducing effects
because this single nucleotide polymorphism (SNP) was of smoking on CYP1A2 the analyses were repeated in
later not genotyped in HapMap [35], we chose another nonsmoking participants only.
SNP in HapMap, rs11854147, which is in linkage dise- We additionally analyzed whether there existed a dif-
2quilibrium with rs762551 (R = 0.886). The SNP ferenceinadjustedmeanBMDvaluesinmenand
rs11854147 was genotyped at the SNP Technology Plat- women with a high consumption of coffee (4 cups or
form at Uppsala University, Sweden [36] using the Illu- more per day) according to their calcium intake: low
mina BeadStation 500GX and the 384-plex Illumina (<600 mg/day), intermediate (600-1200 mg/day) and
Golden Gate assay (Illumina Inc., San Diego, CA, USA) high (>1200 mg/day) total calcium intake (including diet
[37]. The sample success rate was 98.8% and the repro- and supplements).
ducibility 100% according to duplicate analysis of 2.4%
of the genotypes. The genotype distribution was in Results
Hardy-Weinberg equilibrium. Characteristics of the participants in relation to con-
sumption of coffee are displayed in Table 1. Half of the
Statistical analyses participants reported consumption of 3 or 4 cups of cof-
We had the possibility to include 717 genotyped partici- fee daily and one fourth reported an intake of more than
pants with both dietary assessment and BMD measure- 4 cups of coffee per day. High consumers of coffee in
ment in our analysis. All statistical calculations were both men and women had a higher intake of energy and
performed using SAS (SAS 9.1; SAS Institute Inc., Cary, nutrients. However, their body mass index (BMI) was
NC). The relation between coffee consumption as a con- similar to that for low consumers of coffee. Self-reported
tinuous variable and BMD was primarily analyzed by leisure physical activity was also comparable between
ordinary linear regression models. We further categor- categories of coffee consumers, whereas current smok-
ized coffee intake by quartiles (0-2 cups/day, 3 cups/day, ing was more prevalent in both men and women with
4 cups/day and more than 4 cups/day), and the least high consumption of coffee compared with those who
square means of BMD for each quartile was estimated drank none or small amounts (0-2 cups) of coffee.
on the basis of the regression estimates using the Gen- After multivariable adjustment, there was a trend of
eral Linear Model (GLM). All estimates were age- decreased BMD at the total proximal femur with
adjusted (at time of the DXA measurement) or adjusted increasing amounts of coffee consumed (p for trend
by a multivariable model. The multivariable model 0.04) (Table 2). Men who consumed 4 cups of coffee or
included age, height, weight, total caloric intake; intakes more per day had a 4% lower BMD at the total proximal
of vitamin D, vitamin A, calcium, alcohol and tea (all femur as compared with men who drank 0-2 cups per
continuous). Categorized variables included in the day (p = 0.04). This difference was not observed in the
model were smoking (never, current, former) and levels female participants. BMD of the femoral neck and tro-
of leisure physical activity (low, medium, high). Physical chanteric region of the proximal femur was reduced by
activity was divided into light and hard exercise and 3-5% in men consuming 4 cups or more of coffee per
classified as number of activities for at least 30 min per day (femoral neck p = 0.05 and trochanter region p =
week. The participant were asked how many times per 0.01 - data not shown). Results for caffeine intake mir-
week he/she performed light (e.g. walking, gardening) rored those for coffee consumption (data not shown).
respectively hard exercise (e.g. running, swimming) for Multivariable-adjusted mean values in rapid and slow
at least 30 min [38]. Based on the responses to these metabolizers (men and women) of coffee with a coffee
questions, three physical activity categories were con- consumption of 4 cups or more per day are displayed in
structed: low, medium, and high. The questions used in Figure 1. Lower (approximately 2-4%) BMD values were
PIVUS were similar to the questions used in the found in rapid metabolizers of caffeine. The differences
Uppsala Longitudinal Study of Adult Men (ULSAM) reached statistical significance at the femoral neck (p =
cohort [39]. The questions in ULSAM have been vali- 0.01) and trochanter region (p = 0.03), but not at the
dated [40]. total proximal femur (p = 0.10) (Figure 1). BecauseHallström et al. Nutrition & Metabolism 2010, 7:12 Page 4 of 9
stTable 1 Baseline characteristics of the participants by amount of coffee consumption at the 1 investigation of the
aPIVUS cohort
Men (n = 359) Women (n = 358)
bCharacteristics Categories of coffee consumption (cups /day) Categories of coffee consumption (cups/day)
0-2 3 4 >4 0-2 3 4 >4
Number of persons 82 81 85 111 92 110 76 80
Mean age at baseline (years) 72.0 ± 0.8 71.8 ± 0.9 71.8 ± 0.8 72.0 ± 0.8 72.1 ± 0.9 72.1 ± 0.9 72.1 ± 0.8 72.2 ± 0.9
Calcium intake (mg/day) 850 ± 323 949 ± 306 1059 ± 392 1118 ± 365 852 ± 260 912 ± 263 962 ± 267 1011 ± 319
Vitamin D intake (μg/day) 5.7 ± 2.1 5.9 ± 2.0 6.4 ± 2.2 7.1 ± 2.9 5.0 ± 1.8 5.1 ± 1.6 5.8 ± 1.8 5.5 ± 2.1 A intake (mg/day) 0.78 ± 0.53 1.0 ± 0.70 0.95 ± 0.64 1.10 ± 0.76 0.78 ± 0.69 0.81 ± 0.53 0.91 ± 0.65 0.84 ± 0.57
Energy intake (kcal/day) 1830 ± 452 1953 ± 421 2102 ± 510 2308 ± 591 1557 ± 404 1698 ± 352 1812 ± 370 1834 ± 457
Weight (kg) 83.9 ± 11.9 80.6 ± 10.3 84.6 ± 14.8 82.8 ± 12.8 68.7 ± 14.5 70.0 ± 13.0 70.2 ± 13.3 69.2 ± 11.8
Height (cm) 175.4 ± 6.0 175.6 ± 5.7 176.3 ± 6.6 175.3 ± 6.8 161.4 ± 6.0 161.3 ± 5.5 161.6 ± 5.2 161.7 ± 5.7
2Body mass index (kg/m ) 27.3 ± 3.7 26.2 ± 3.3 27.2 ± 4.2 26.9 ± 3.7 26.4 ± 5.5 26.9 ± 4.4 26.9 ± 5.1 26.5 ± 4.4
Alcohol use (g/day) 11.0 ± 10.0 7.7 ± 7.5 9.5 ± 9.7 8.3 ± 8.7 5.0 ± 5.7 4.1 ± 4.6 4.8 ± 4.8 4.1 ± 4.7
Smoking status
Never 34/82 (41) 42/81 (52) 32/85 (38) 49/111 (44) 49/92 (53) 58/110 (53) 48/76 (63) 37/80 (46)
Current 3/82 (4) 6/81 (7) 5/85 (6) 15/111 (14) 10/92 (11) 10/110 (9) 7/76 (9) 14/80 (18)
Former 45/82 (55) 33/81 (41) 48/85 (56) 46/111 (41) 33/92 (36) 42/110 (32) 21/76 (28) 29/80 (36)
Levels of physical activity
Low 9/82 (11) 1/81 (1) 4/85 (5) 12/111 (11) 9/92 (10) 5/110 (5) 3/76 (4) 3/80 (4)
Medium 37/82 (45) 41/81 (51) 46/85 (54) 52/111 (47) 46/92 (50) 56/110 (51) 35/76 (46) 39/80 (49)
High 35/82 (43) 38/81 (47) 31/85 (36) 45/111 (41) 37/92 (40) 46/110 (42) 35/76 (46) 34/80 (43)
a bAll values are mean ± SD (continuous variables) or frequencies (categorical variables). Values in parentheses are frequencies expressed in percent. The volume
of one cup of coffee is 150 mL
smoking is known to induce CYP1A2, current smokers risk group more prone to develop osteoporosis might,
(n = 69) were excluded in an extended analysis of the thus, have been identified.
cohort. The results of this analysis remained essentially The observed decrease in BMD in male high consu-
unchanged in terms of effects upon BMD (data not mers of coffee could be estimated to correspond to an
shown). There were, furthermore, no statistical differ- approximately 30% increased risk of hip fracture, which
ences between slow and rapid metabolizers with a low wouldimplyaconsiderableincreaseinviewofpublic
consumption of coffee or between rapid metabolizers health [41]. This increased risk might have impact on
with a low consumption of coffee and slow metabolizers total osteoporotic fracture health economy. This is illu-
with a high consumption (data not shown). strated by the fact that the number of hip fractures
High consumers (men and women) of coffee (4 cups worldwide in the year of 2000 was estimated to 1.6 mil-
or more per day) with a high calcium intake (more than lion [42]. The global cost for hip fractures is rising and
1200 mg per day) did not have higher adjusted average by 2050 it has been estimated to be about 132 billion
BMD values compared with those with high coffee con- US dollars [43].
sumption and low (<600 mg/day) or intermediate (600- Earlier studies in men [12,15-21] have not observed
1200 mg/day) calcium intake (Data not shown). Finally, any statistically significant relation between consump-
tea was consumed by 439 participants (about 60%) in tion of coffee and BMD. It should be noted, however,
the study. Tea consumption was not associated with that some of the studies were small [12,15,21]. In most
multivariable-adjusted BMD (parameter estimate per studies [17-21] the exposure was defined as caffeine
cup of tea -0.0014 (95% confidence interval -0.0106, intake from both coffee and tea. This approach may not
0.0078; p = .77). be optimal because both beverages contain several other
bioactive substances that may modify the effects of caf-
Discussion feine. Furthermore, many of the earlier studies do not
In this cohort the consumption of coffee was high. We clearly state the exposure as amount of coffee or caf-
observed a decrease in BMD of the proximal femur in feine consumed [15,17,18,20]. When stated, the average
men consuming 4 cups of coffee or more daily. In high intake of coffee/caffeine varied from approximately 200
consumers of coffee, rapid metabolizers had lower BMD mg caffeine per day [19,21] or less than two cups of cof-
values than slow metabolizers of caffeine. A potential fee per day [12] to 3 cups per day in one study [16].Hallström et al. Nutrition & Metabolism 2010, 7:12 Page 5 of 9
aTable 2 Age-adjusted and multivariable-adjusted bone mineral density (BMD) in the proximal femur (mean and 95%
CI) of the PIVUS cohort by amount of coffee consumption
bCategories of coffee consumption (cups /day)
c0-2 3 4 >4 b (95% CI) per cup
p for trend
All participants (n = 717)
n = 174 n = 191 n = 161 n = 191
Age-adjusted 0.96 (0.94, 0.98) 0.93 (0.91, 0.95) 0.95 (0.93, 0.97) 0.95 (0.92, 0.97) 0.0006
(-0.0061, 0.0074)
Reference p = 0.06 p = 0.59 p = 0.44 p = 0.85
Multivariate-adjusted 0.96 (0.94, 0.98) 0.94 (0.93, 0.96) 0.94 (0.92, 0.96) 0.94 (0.92, 0.96) -0.0064
(-0.0127, -0.0001)
Reference p = 0.15 p = 0.09 p = 0.08 p = 0.04
Men (n = 359)
n = 82 n = 81 n = 85 n = 111
Age-adjusted 1.05 (1.02, 1.09) 1.00 (0.97, 1.04) 1.01 (0.98, 1.04) 1.01 (0.98, 1.03) -0.0054
(-0.0133, 0.0025)
Reference p = 0.03 p = 0.07 p = 0.03 p = 0.18
Multivariate-adjusted 1.05 (1.02, 1.08) 1.02 (0.99, 1.04) 1.01 (0.98, 1.03) 1.01 (0.98, 1.03) -0.0072
(-0.0151, 0.0008)
Reference p = 0.10 p = 0.04 p = 0.04 p = 0.08
Women (n = 358)
n = 92 n = 110 n = 76 n = 80
Age-adjusted 0.87 (0.85, 0.90) 0.87 (0.85, 0.90) 0.88 (0.85, 0.91) 0.86 (0.83, 0.89) -0.0043
(-0.0136, 0.0054)
Reference p = 0.96 p = 0.72 p = 0.57 p = 0.40
Multivariate-adjusted 0.87 (0.85, 0.90) 0.87 (0.85, 0.90) 0.88 (0.85, 0.91) 0.86 (0.84, 0.89) -0.0041
(-0.0138, 0.0056)
Reference p = 0.91 p = 0.73 p = 0.62 p = 0.41
a Adjusted by age at the BMD-measurement, height, weight, total caloric intake, vitamin D intake, vitamin A intake, calcium intake, alcohol intake, intake of tea
b c(all continuous), smoking (never, current, former) and levels of leisure physical activity (low, medium, high) The volume of one cup of coffee is 150 mL Per cup
of coffee
Figure 1 Mean adjusted BMD (bone mineral density) of the total proximal femur in men and women with a high consumption of
coffee (4 cups or more per day) by CYP1A2 polymorphism. The error bars indicate 95% confidence intervals (CI) and the p-values refer to
comparisons between slow and rapid metabolizers at each site. Mean values are adjusted by age at the BMD measurement, height, weight, total
caloric intake, vitamin D intake, vitamin A intake, calcium intake, alcohol intake, intake of tea (all continuous), smoking (never, current, former)
and levels of leisure physical activity (low, medium, high).Hallström et al. Nutrition & Metabolism 2010, 7:12 Page 6 of 9
In our study, compared to most other studies, mean osteoblasts, which could enhance the rate of osteoblast
intake of caffeine and consumption of coffee was higher: apoptosis. In addition, Lu et al (2008) [61] has demon-
367 mg/day and 3.2 cups/day, respectively. strated that cell viability also decreased in human osteo-
In the majority of the studies of women no relation blasts treated with caffeine in a dose-dependent manner
between consumption of coffee or intake of caffeine and mainly due to apoptosis. Zhou et al (2009) [62] hypothe-
BMD has been detected [6,7,13,14]. Nevertheless, a sise, however, that bone marrow-derived mesenchymal
weak negative relation between coffee or caffeine and stem cells, which are precursor cells of osteoblasts, may
BMD has been observed [9,11,22,44-48] but the relation be the real target cells of caffeine-induced osteoporosis
between BMD and intake of coffee/caffeine has been in vivo. However, it remains to be demonstrated
attenuated by adequate intake of milk/calcium [9,22,47]. whether a mechanism including direct effects of caffeine
Our results do not support these latter findings but few or its metabolites on cells involved in the remodelling
of our participants had a low calcium intake. In general, process could be of importance also in vivo at dosages
the studies in women thus provided limited evidence for of relevance to humans.
the existence of a relation between intake of coffee/caf- It has been demonstrated that both the parent com-
feine and effects on BMD, which is accordance with our pound, caffeine, as well as paraxanthine, might be tera-
results. It should be noted that as in the studies of men, togenic after administration of very high doses in mice
many of the studies in women were small [9,49-57]. In with skeletal malformations as a consequence [63]. Caf-
addition, no separate analyses of coffee and tea were feine is cleared more quickly than paraxanthine and 8
carried out in the majority of studies of women hours after caffeine intake, plasma concentrations of
[8-10,44,45,48-56,58,59]. Average intake of coffee or caf- paraxanthine levels exceed those of caffeine [64]. With
feine seems to have been low or modest in some studies long-term exposure of high doses of there is
[10,44,53,55,56], i.e., lower than in the present substantial accumulation of paraxanthine [65,66]. Para-
investigation. xanthine has in vitro been found to be a potent suppres-
There is evidence for females having lower activity of sor of transforming growth factor beta (TGF-b) [67],
CYP1A2 than men [27]. With a higher CYP1A2 activity which stimulates bone formation, and TGF-b deficiency
in men, caffeine will be more rapidly metabolized and may result in osteoporosis [68]. Interestingly, para-
the concentrations of metabolites like paraxanthine will xanthine has been found to be the most powerful phar-
become higher in relation to the concentration of caf- macological repressor of hepatocellular TGF-b
feine. The deleterious effect of coffee consumption on dependent connective tissue growth factor expression
bone may be an effect of caffeine metabolites. Consis- among the drug family of methylxanthines, including
tent with this theory is that we observed lower BMD caffeine [67]. The major caffeine derivatives, including
among rapid compared to slow metabolizers of caffeine paraxanthine, have common mechanisms of action, i.e.
with a high coffee consumption. Moreover, we found competitive antagonism of the adenosine interaction
lower BMD among male high consumers of coffee but with A and A receptors. Deactivation of the adenosine1 2
not among such women, an observation that may be receptors, which are expressed in bone cells, can result
explained by higher CYP1A2 activity in men [27]. In in reduced bone formation [69].
addition, we did not find any statistical differences
between slow and rapid metabolizers with a low con- Advantages and limitations of our study
sumption of coffee or between slow metabolizers with a To our knowledge, this is one of few population-based
high consumption of coffee and rapid metabolizers with studies investigating possible effects of coffee and tea
a low consumption. Our results may thus indicate that a consumption on BMD in both men and women. In con-
certain level of metabolites must be reached in order to trasttomostotherstudies, the majority of the partici-
observe a negative effect on BMD. There are, however, pants in our study consumed high amounts of coffee.
no published data regarding effects of metabolites of We had a sufficient number of participants to detect
caffeine on BMD. Therefore more studies are clearly even modest associations. An additional strength is that
warranted in order to investigate possible mechanisms we did not focus on caffeine intake but on the exposure
of interactions regarding caffeine intake and CYP1A2 of coffee and tea separately. This distinction may be
genotype in relation to BMD. How caffeine or its meta- important because some studies have indicated that con-
bolites exert effects on bone can theoretically be sumptionofteacouldhaveapositiveinfluenceon
explained by other mechanisms than by reduced renal BMD, which could counteract the negative influence of
calcium conservation. According to some in vitro stu- coffee. Tea consumption in our study was low and
dies, caffeine may interfere with bone remodelling pro- adjusted for in the statistical analyses. The possible
cess. Tsuang et al (2006) [60] suggested that caffeine modification by genotype for CYP1A2 inducibility has
may have deleterious effect on the viability of rat not previously been investigated. We also had theHallström et al. Nutrition & Metabolism 2010, 7:12 Page 7 of 9
possibility to consider several conceivable covariates in consumers of coffee with rapid metabolism of caffeine,
the analysis, including nutrients, physical activity beha- suggesting that this group of coffee consumers might be
vior and smoking. at special risk of bone loss.
This study nevertheless has several potential limita-
tions. In this study we have measured BMD in the proxi-
mal femur only. We refrained from including BMD We thank Tomas Axelsson, Torbjörn Öst and Marie Lindersson at the SNP
measurements of the spine since spondylosis is common Technology Platform in Uppsala, Sweden for assistance with the genotyping.
This study was supported by grants from the Swedish Research Council. Thein elderly individuals, and this condition can confound
SNP genotyping was supported by the Knut and Alice Wallenberg
the relative weak association between BMD and coffee as foundation and Uppsala University.
well as the comparison between sexes. As the measure-
Author detailsment of BMD was on average performed 2 years after the
1Research and Development Department, Toxicology Division, National Food
dietary investigation, the follow-up time was limited. 2Administration, Box 622, SE-751 26 Uppsala, Sweden. Uppsala Clinical
However, the optimal time between measurements of Research Center (UCR), University Hospital, SE-751 85 Uppsala, Sweden.
3Department of Medical Sciences, Section of Clinical Pharmacology, Uppsalacoffee consumption and BMD is currently not known.
4University, SE-751 85 Uppsala, Sweden. Department of Medical Sciences,
Nevertheless, it should be noted that earlier studies on Section of Acute and Internal Medicine, Uppsala University, SE-751 85
5skeletal effects by an exposure that affects calcium meta- Uppsala, Sweden. Department of Medical Sciences, Molecular Medicine,
6Uppsala University, SE-751 85 Uppsala, Sweden. Department of Surgicalbolism indicate a lag period of 2-3 years before a steady
Sciences, Section of Orthopedics, Uppsala University, SE-751 85 Uppsala,
state of bone turnover and BMD is reached [70,71]. Sweden.
Statistically significant differences in BMD between
Authors’ contributionshigh consumers who were rapid metabolizers and those
The authors’ contributions were as follows - HH and KM: designed the study;
who were slow metabolizers of caffeine were generally HH: analyzed the data and drafted the manuscript; LL: recruited the
confined to the whole study group of both men and participants, obtained funding, collected data and is principal investigator for
the cohort; A-CS: organized the genotyping; HM and AG contributed to thewomen, probably because statistical power was too low
study design and performance, and assisted with the editing of the
to attain statistical significance in the groups of each manuscript and KM revised the manuscript, supervised the study, collected
gender. There were, however, clear tendencies of a data and obtained funding. All authors have read and approved the final
manuscript.lower BMD in high consuming males who were rapid
metabolizers. In women the same pattern could also be Competing interests
observed. The authors declare that they have no competing interests.
Because the exposure measurement was based on a
Received: 7 December 2009 Accepted: 22 February 2010
single dietary measurement, there may be some degree Published: 22 February 2010
of error in the measurement. The 7-day dietary record-
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